Despite its name, the false killer whale is not a close relative of the killer whale, or orca.

The scientific name of the false killer whale, crassidens, means ‘thick-tooth’, referring to the animal’s formidable-looking, conical teeth.

A highly efficient predator, the false killer whale feeds on a wide range of prey and may even hunt dolphins and whales.

The false killer whale develops long-term social bonds and has been known to share prey with its companions.

The false killer whale is classified as Data Deficient (DD) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

Despite its name, the false killer whale (Pseudorca crassidens) is not a close relative of the killer whale or orca (Orcinus orca), and any resemblance to this species is relatively superficial (2) (4) (5). The name of the false killer whale instead comes from a similarity between the skulls of these two species (4).

The false killer whale’s body is long and slender, with a tall, backwardly-curving dorsal fin and uniquely shaped flippers that possess a large bulge at the midpoint, reminiscent of an elbow (6) (7). The head tapers into a long, rounded snout, which overhangs the lower jaw and is marked with a crease running above the mouthline (7). The jaws are armed with 8 to 11 pairs of large, formidable-looking, conical teeth, from which the false killer whale derives its Latin name, crassidens, meaning 'thick-tooth' (7).

The body of the false killer whale is almost uniformly dark grey to black, with the exception of faint grey marks on the heads of some individuals and a whitish chest patch between the flippers (4) (7).

The false killer whale is widespread throughout tropical and sub-tropical waters (1) (5).

Although there are occasional records of the false killer whale from higher latitudes, such as around Norway and Alaska, there are no known populations in temperate waters, and these records are likely to represent stray individuals (5).

Although the false killer whale is most commonly found in open ocean waters, it also frequents areas around oceanic islands such as Hawaii, and may enter semi-enclosed seas such as the Mediterranean (5) (7) (8).

This rapid locomotion also makes the false killer whale a highly efficient predator, and it feeds on an array of different prey items. Depending on its location, the prey of this species may include squid and a variety of large pelagic fish, including several species of tuna, wahoo (Acanthocybium solandri) and mahi mahi (Coryphaena hippurus) (5) (9). Groups of false killer whales have also been observed feeding on smaller dolphins being released from purse seine nets and harassing or possibly attacking humpback and sperm whales (4) (5) (6).

A highly social species, the false killer whale usually forms groups of between 10 and 50 individuals of mixed sex and age. However, these may occasionally merge into large aggregations of several hundred animals (6). Individuals appear to communicate extensively by producing an incredibly diverse array of clicks and whistles (2). Sound is also employed by the false killer whale in the form of echolocation, which is used to sense its environment and locate prey (4). The false killer whale has been found to develop long-term social bonds and to share prey with its companions, or even sometimes with humans (8).

The false killer whale is believed to breed throughout the year, but births may peak at different times depending on the location (2). After a gestation period of about 15.5 months, the calf is born measuring up to 2 metres in length. For the first 18 to 24 months, the calf is fed on milk (2).

The female false killer whale is though to reach sexual maturity at 8 to 11 years, while the male may mature slightly later (2). The lifespan of the false killer whale is not well known, but estimates based on ageing individuals by their teeth give a maximum age of at least 62 years for females and 57 years for males (4).

In general, the population status of the false killer whale is poorly known. As a top predator it does not appear to be particularly abundant at any location, and it may therefore be severely affected by relatively low-grade threats (1). Any threats to this species may also be exacerbated by its long lifespan and slow reproduction rate, which mean that its populations would be very slow to recover from declines (8).

The false killer whale faces three main threats: bycatch in fisheries; the worldwide decline in the number and size of the predatory fish species that constitute a major part of its diet; and the accumulation of high levels of persistent organic pollutants, which can potentially lower the false killer whale’s resistance to disease (1) (4) (5) (8). The false killer whale is also well-known for taking bait or catches from longlines, which has led to retaliatory cullings, despite the fact that many of the whales are killed by becoming caught on the hooks and drowned (1).

Huge numbers of false killer whales, in one case over 800, are often involved in beach strandings (6). This species has been recorded ingesting discarded plastic (1) (4), and may also be vulnerable to loud man-made sounds such as those produced by navy sonar and seismic exploration (1) (5).

A small, resident population of false killer whales in Hawaiian waters is the best known in the world. This population has declined dramatically in the last 20 years, and is a high priority for research programmes in Hawaii (8).

The false killer whale is a relatively poorly known species, and more research is needed into its populations, migratory movements and levels of bycatch (1). It is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this species should be carefully controlled (3). The Hawaiian insular population of false killer whales has been proposed for listing as ‘Endangered’ under the U.S. Endangered Species Act (10).

Research underway for the resident false killer whales in Hawaii includes satellite tagging, photo-identification, and monitoring of bycatch in longline fisheries (8).